170 THE COCKROACH : 



and spot (nucleus and nucleolus), which were at first very 

 plain, disappear. A vitelline membrane is secreted by the 

 inner surface, and a chitinous chorion by the outer surface of 



the egg-follicle. 



The lowest egg in an ovarian tube is nearly or altogether of 

 the full size ; it is of elongate-oval figure, and slightly curved, 

 the convexity being turned towards the uterus. It is filled 

 with a clear albuminous fluid, which mainly consists of yolk. 

 The chorion now forms a transparent yellowish capsule, which 

 under the microscope appears to be divided up into very many 

 polygonal areas, defined by rows of fine dots. These areas 

 probably correspond to as many follicular cells. The convex 

 surface of the chorion is perforated by numerous micropyles, 

 fine pores through which it is probable the spermatozoa gain 

 access to the interior of the egg. 



The uterus has a muscular wall and a chitinous lining. Two 

 repeatedly branched colleterial glands open into its under side. 

 Of these the left is much the larger, and overlies the other. 

 It consists of many clichotomous tubes, some of which are a 



*- 



little dilated at their blind ends. The gland is much entangled 

 with fat-cells, which make it difficult to unravel. The right 

 gland is probably of no functional importance ; the left gland 

 is filled with a milky substance, containing many crystals and 

 a coagulable fluid, out of both of which the egg-capsule is 

 formed.* 



At its hinder end the uterus opens by a median vertical slit, 

 which lies in the 8th sternum, into a genital pouch which 

 represents part of the external integument, folded back far into 

 the interior of the abdomen. (See fig. 96.) Upon the dorsal 

 wall of the genital pouch the orifice of the sperniatheca is 

 situated.-)* This is a short tube dilated at the end, and wound 



* The crystals have been supposed to consist of oxalate of lime (Duchamp, Rev. 

 des sci. nat. Montpellier, Tom. VIII.). Hallez observes that they are prismatic, with 

 rhombic base, the angles truncated. They are insoluble in water and weak nitric 

 acid, but dissolve rapidly in strong sulphuric acid without liberation of gas, and still 

 more rapidly in caustic potash. (Compt. Rend., Aug., 1S85.) 



f It is usually stated that the spermatheca of the Cockroach opens into the 

 uterus, as it does in most other Insects, but this is not true. Locusts and Grass- 

 hoppers have the outlet of the spermatheca placed as in the Cockroach ; in other 

 European Orthoptera, it lies upon the dorsal wall of the uterus. (Berlese, loc. cit., 

 p. 273.) 



